The present invention relates to a method for increasing the molecular weight of a polymer.
The molecular weight of polymers may be increased for a number of reasons. For instance, in some processes lower molecular weight polymer may be more readily processed in the melt phase, but the resultant products may exhibit deficiencies in properties due to the low molecular weight. In such situations, it may be possible to process the polymer using the lower molecular weight, and to subsequently increase the molecular weight of the polymer e.g. by cross-linking the polymer. In other instances, several processes may be operated from a single source of polymer but one of the processes may require a higher molecular weight polymer than the other processes. It may also be desireable to increase polymer molecular weight because the process for manufacturing the polymer provides a lower molecular weight polymer than is desired or because the polymer that is available commercially is of lower molecular weight than is required.
A variety of methods are known for increasing the molecular weight of polymers, including subjecting the polymer to cross-linking processes. For example, polyolefins may be cross-linked by admixing the polymer with an organic peroxide and then melt extruding the polymer or by admixing the polymer with a vinyl silane, extruding the polymer and then subjecting the polymer to moisture. Condensation polymers such as polyamide may be cross-linked by heating the polymer in the presence of a catalyst, such as ammonium or metal hypophosphite, phosphoric acid, triphenyl phosphite and p-toluenesulphonic acid, and removing water.
It is desired to provide a process to increase the molecular weight of polymer in an efficient manner.